Safety Factor


Quick
The safety factor may also be called the factor of safety. The safety factor may be abbreviated by F.S., SF, or n. The safety factor is a ratio of the ultimate capacity to the allowable capacity. Ultimate can be thought of as the maximum value that can be tolerated by a part without failure. Allowable can be though of as the maximum value to be experienced by the part for the duration of its working life.


Equations
safety factor =
ultimate load
allowable load

and also

safety factor =
ultimate stress
allowable stress


Implications

Understanding the definitions of ultimate and allowable, it can be seen that as the safety factor decreases, the possibility of failure increases. Conversely, as the safety factor increases, the part becomes less economical and functional. Therefore, the safety factor must be chosen appropriately to obtain the correct balance between reliability, economy, and functionality for a given application.

Deciding upon a reasonable safety factor is dependent upon various criteria such as the following: The selection of a reasonable safety factor requires a good knowledge of design, a thorough understanding of the strength of the material, and application engineering experience.



Related
▪ L - Design Factor and Safety Factor